1. Field of Invention
The present invention relates generally to current or voltage reference generating circuits. More particularly, it relates to a circuit and method for generating a start-up pulse for such reference circuits.
2. Description of Related Art
Many integrated circuits use reference generating circuits to provide stable current or voltage references. Current mirror reference generating circuits are known in the art. A circuit with one or more current mirrors is configured to seek its own current, thereby creating a current source independent of temperature and circuit processes. A problem with many circuit configurations is that they may settle in one of two steady states upon initial power-up. In one steady state the circuit conducts to provide its design value reference output. In a second steady state, however, the circuit remains in a non-conducting state and does not provide the desired reference output.
To overcome the problem of a non-conducting current steady state on initial power-up, many circuits use an initial start-up pulse to force the reference generating circuit into its desired operating state. Existing circuits require this start-up pulse to be from an external source such as a system-wide central processing unit (CPU). However, some integrated circuit devices must operate independently of any direct external power source.
One example is a remote radio frequency identification circuit. These remotely powered integrated circuits cannot access any externally applied start-up pulse used to force the reference generating circuit to a conducting state. Further, other on-chip systems such as a CPU are also in indeterminate states on initial power-up and so cannot be relied upon to provide the needed start-up pulse. Therefore the need exists for a circuit that reliably generates the required start-up pulse within the integrated circuit itself.
A related concern for independently operating integrated circuits is to minimize power consumption. If no start-up pulse is required, for example, no power need be used to supply one. Similarly, once the reference circuit receives a required start-up pulse, the pulse generating circuit should be turned off. Therefore a circuit that provides a start-up pulse only when required, and minimizes current drain after providing the pulse, is desirable.